The communications industry is rapidly changing to adjust to emerging technologies and ever increasing customer demand. This customer demand for new applications and increased performance of existing applications is driving communications network and system providers to employ networks and systems having greater speed and capacity (e.g., greater bandwidth). In trying to achieve these goals, a common approach taken by many communications providers is to use packet switching technology. Increasingly, public and private communications networks are being built and expanded using various packet technologies, such as Internet Protocol (IP).
A network device, such as a switch or router, typically receives, processes, and forwards or discards a packet based on one or more criteria, including the type of protocol used by the packet, addresses of the packet (e.g., source, destination, group), and type or quality of service requested. Additionally, one or more security operations are typically performed on each packet. But before these operations can be performed, a packet classification operation must typically be performed on the packet.
Packet classification as required for, inter alia, access control lists (ACLs) and forwarding decisions, is a demanding part of switch and router design. The packet classification of a received packet is increasingly becoming more difficult due to ever increasing packet rates and number of packet classifications. For example, ACLs require matching packets on a subset of fields of the packet flow label, with the semantics of a sequential search through the ACL rules. IP forwarding requires a longest prefix match.
Known approaches of packet classification include using custom application-specific integrated circuits (ASICs), custom circuitry, software or firmware controlled processors, binary and ternary content-addressable memories (CAMs). The use of programmable software or firmware have advantages as they provide some level of flexibility, which becomes especially important as new protocols and services are added to existing network. Customer typically desire to use their existing hardware (e.g., routers, switches, etc.) to support these new protocols and services. However, known software and firmware implementations are relatively slow, and typically place a performance bound which may be incompatible with new requirements. Various applications that use packet classification, such as Security Access Control, Quality of Service, etc., typically need to perform many matches on source and destination port numbers, protocol and/or other header fields, etc. in order to identify a corresponding netflow.
In a known prior system, one or more fields are extracted from a received packet. These one or more extracted fields typically include source and destination addresses, port numbers, and possibly other fields, typically included in the header or flow label of a packet. These extracted fields are provided in their native format, possibly along with other data, to a CAM, which performs a lookup operation in performing the packet classification. Because CAMs are expensive, especially in terms of space and power consumption and are limited in the width of an input lookup word, one known system preprocesses, via one or more logical functions or operations, certain information contained in a packet to generate a vector that is used as part of a lookup word. This vector reduces the number of bits that would be required if the entire native information was included in the lookup word.
Many hardware implementations use ternary content addressable memories (TCAMs) to implement ACLs. TCAMs have worked well as they implement order dependent ACLs efficiently. However, TCAMs suffer from many problems that are becoming critical with faster and bigger designs going forward. TCAMs have minimal latency, but consume lot of power and generate a lot of heat, which is typically proportional to the width and activity of the TCAM. Moreover, designers of systems increasingly desire to perform lookup operations on strings of longer length, such as that caused by switching from 32 bit IPv4 addresses to 128 bit IPv6 addresses, while the widths of lookup words for associative memories remain comparatively small. New methods and apparatus are needed to perform lookup operations.